JP2006118011A - Steel having excellent seaside weather resistance and structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost steel having excellent seaside weather resistance and capable of exhibiting excellent weather resistance even in a severe corrosive environment where the amount of flying salt exceeds 1 mdd (mg/dm<SP>2</SP>/day). <P>SOLUTION: The steel has a composition comprising, by mass, 0.001 to 0.15% C, ≤2.5% Si, >0.5 to 2.5% Mn, <0.03% P, ≤0.005% S, 0.05 to 1.0% Cu, 0.01 to 0.5% Ni, 0.01 to 3.0% Cr, 0.003 to 2.5% Al, and 0.001 to 0.1% N, Sn and/or Sb of 0.03 to 0.50%, further comprising one or more kinds of metals selected from 0.01 to 0.3% Ti, 0.01 to 0.1% Nb, 0.01 to 1.0% Mo, 0.01 to 1.0% W, 0.01 to 1.0% V, 0.0001 to 0.1% Ca, 0.0001 to 0.1% Mg and 0.0001 to 0.02% rare earth metals, and the balance Fe with impurities, and in which the mass ratio of Ni/Cu is ≤0.5. The surface of the steel may be coated with a corrosion prevention coating. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is weather resistant in the sense that it can be used as a minimum maintenance material even in an environment where there is a large amount of incoming salt, such as a beach area or an area where snow melting salt / freezing agents are sprayed. Is referred to as “seaside weather resistance”) (ie, steel material excellent in beach weather resistance) and a structure made from this steel material.

  In general, when weathering steel is exposed to an atmospheric corrosive environment, a protective rust layer is formed on the surface, and the subsequent corrosion of steel is suppressed, thereby exhibiting weather resistance. Therefore, the weather-resistant steel is used for structures such as bridges as a minimum maintenance steel that can be used as it is without being painted.

  However, in environments where there is a large amount of incoming salt, such as in the coastal area and inland areas where snow melting salt / freezing agents are sprayed, a protective rust layer is not formed on the surface of the weathering steel, and corrosion occurs. The effect which suppresses is not demonstrated. For this reason, it was not possible to use a weather-resistant steel material that has not been painted on the beach.

In weathering steel standardized by Japanese Industrial Standards (JIS) (JIS G3114: Weathering hot rolled steel for welded structures), the amount of incoming salt is 0.05 mg / dm ² / day (0.05 mdd) as NaCl. In the above area, that is, the beach area, corrosion loss due to the occurrence of scale-like rust and layered rust is large, so it cannot be used without painting (Ministry of Construction, Public Works Research Institute, (Co) Steel Club, (Company ) Japan Bridge Construction Association: Joint Research Report on the Application of Weatherproof Steel to Bridges (XX)-Design and Construction Guidelines for Uncoated Weatherproof Bridges (Revised Version-1993.3)).

  For this reason, in a salty environment such as a beach area, it is common to use ordinary steel that is coated with ordinary steel. However, the bridges constructed in the coastal areas near the river mouths and roads such as mountainous areas where snowmelt salt / freezing agents are sprayed are extremely corroded, and it is necessary to repaint every 10 years due to coating deterioration due to corrosion. . Since these repaints require a great amount of man-hours and enormous costs for maintenance, there is a strong demand for steel materials with excellent beach weather resistance that can be used without painting even in beach areas.

  Recently, Ni-based high weathering steel with about 1% to 3% Ni added has been developed and put to practical use. However, with such addition of Ni alone, the amount of incoming salt exceeds 0.3 to 0.4 mdd. So it has proven difficult to apply.

  Since corrosion of steel materials becomes more severe as the amount of flying salt increases, a weather-resistant steel material corresponding to the amount of flying salt is required from the viewpoint of corrosion resistance and economy. Moreover, even if it is called a bridge, the corrosive environment of steel materials is not the same by the place and site | part used. For example, outside the girders, they are exposed to rainfall, condensed water and sunlight. On the other hand, inside the girders, they are exposed to condensed water, but there is no rain. In general, it is said that in an environment where the amount of incoming salt is large, the inside of the girders without rain catches is more corroded than the outside of the girders washed with rain.

  Also, in an environment where snow melting salt / freezing agent is sprayed on the road, the salt is wound up on the running car and adheres to the bridge supporting the road, creating a severe corrosive environment. Furthermore, the eaves under the eaves a little away from the coast are also exposed to severe salt damage environments, and in such areas, the amount of incoming salt becomes a severe corrosive environment with 1 mdd or more.

Steel materials that prevent corrosion in environments with a high amount of incoming salt have also been developed.
For example, Patent Document 1 proposes a weather-resistant steel material with an increased chromium (Cr) content, and Patent Document 2 proposes a weather-resistant steel material with an increased nickel (Ni) content.

However, although Cr can improve the weather resistance in a region where the amount of incoming salt is below a certain level, Cr deteriorates the weather resistance in a severe salt environment exceeding that.
On the other hand, when the Ni content is increased, the weather resistance is improved to some extent, but the cost of the steel material itself becomes high, and the material used for applications such as bridges becomes expensive. In order to avoid this, if the Ni content is reduced, the weather resistance will not be improved so much, and if the amount of incoming salt is high, layered peeling rust will form on the surface of the steel material, corrosion will be remarkable, and it will be used for long periods The problem of being unbearable arises.

  The inventors of the present invention have previously proposed a steel material having beach weather resistance in which Cu, Ni, and Cr are combined and contained in Patent Document 3. However, although only a few percent of these elements can improve the weather resistance compared to JIS weather resistant steel, it has sufficient weather resistance in extremely severe environments where the amount of incoming salt exceeds 1 mdd. It cannot be demonstrated and further improvements are needed.

  Patent Document 4 proposes a welded structural steel containing P, Ni, Mo, Sb, Sn, and the like, and Patent Document 5 proposes a highly weather-resistant steel material containing Cu, Ni, and Sb. The former steel for welded structure has a problem that weldability is not sufficient because the P content is increased in order to obtain weather resistance in an environment with a large amount of incoming salt. The latter high weathering steel material is said to have good weather resistance in an environment with an incoming salt content of 0.8 mdd, but there is a problem that the weather resistance is not sufficient in a severe corrosive environment exceeding 1 mdd.

  Patent Document 6 proposes an acid dew-point corrosion steel having improved corrosion resistance by containing Cu, Ni, Cr, Sn, Sb, etc., and has excellent corrosion resistance against acid dew point corrosion in a chimney or a heat exchanger. Is demonstrating. However, there is a problem that the weather resistance is not sufficient in an air corrosive environment in which the amount of incoming salt exceeds 1 mdd.

JP-A-9-176790 JP-A-5-51668 JP 2000-297343 A Japanese Patent Laid-Open No. 10-251797 JP 2002-53929 A Japanese Patent Laid-Open No. 9-25536

  The present invention aims to solve the problems inherent in conventional weathering steel, etc., in an environment where there is a large amount of incoming salt (especially in coastal areas or areas where snowmelt salt / freezing agents are sprayed) (particularly An object of the present invention is to provide a low-cost steel material and a structure that can exhibit excellent weather resistance even under a severe corrosive environment exceeding 1 mdd) and that have excellent beach weather resistance.

As already reported by one of the present inventors ("Materials and Environment", Vol. 43 (1994), No. 1, p. 26), the rust layer has a protective property in weathering steel. This is because a rust layer made of fine α- (Fe _1-x Cr _x ) OOH in which part is replaced with Cr is formed. However, as described above, the addition of Cr is effective in improving the weather resistance in an environment where the amount of incoming salt is relatively small, but in the environment where the amount of incoming salt is large, the weather resistance is deteriorated conversely. On the other hand, it has been considered that the addition of Ni is effective for improving the weather resistance in an area where the amount of incoming salt is large.

Based on these findings, the present inventors have examined corrosion in an environment with a large amount of incoming salt. As a result, in such an environment, repeated drying and wetting of the FeCl ₃ solution became an essential condition, and Fe ³⁺ It has been found that corrosion is accelerated when pH is lowered by hydrolysis and Fe ³⁺ acts as an oxidizing agent. The corrosion reaction at this time is expressed by the following equation.

Cathode reaction: Fe ³⁺ + e ⁻ → Fe ²⁺ (Fe ³⁺ reduction reaction)
Of course, in addition to this reaction, 2H ₂ O + O ₂ + 2e ⁻ → 4OH ⁻
2H ⁺ + 2e ⁻ → H ₂
The cathodic reaction also occurs.

On the other hand, for the above reduction reaction, anode reaction: Fe → Fe ²⁺ + 2e ⁻ (Fe dissolution reaction)
Also happens. Therefore, the overall reaction of corrosion is
2Fe ³⁺ + Fe → 3Fe 2 ⁺ ... Reaction 1
It becomes.

The Fe ²⁺ produced by the reaction 1 is oxidized to Fe ³⁺ by air oxidation, and the produced Fe ³⁺ accelerates corrosion as an oxidizing agent again. At this time, the reaction rate of air oxidation of Fe ²⁺ is generally slow in a low pH environment, but is accelerated in a concentrated chloride solution, and Fe ³⁺ is easily generated. It has been found that due to such a cyclic reaction, in an environment where the amount of incoming salt is very large, Fe ³⁺ is always supplied, corrosion of steel is accelerated, and corrosion resistance is significantly deteriorated.

  In this way, in an environment where the amount of incoming salt is very large, protection by the rust layer cannot be expected, so it is effective to slow the anodic dissolution reaction of the steel itself. In other words, in an environment where the amount of flying salt is very high, Cr-containing steel accelerates the anodic dissolution reaction, so the weather resistance deteriorates, whereas Ni-containing steel delays the anodic dissolution reaction. Weather resistance is expected to improve.

As a result of examining the influence on the weather resistance of various alloy elements based on the above-mentioned mechanism of corrosion in a salt environment, the following knowledge was obtained.
(A) Sn dissolves as ^{Sn 2+,} by lowering the concentration of ^{Fe 3+} by ^{2Fe 3+ + Sn 2+ → 2Fe 2+} + Sn 4+ comprising reaction, suppressing a reaction 1. Sn also has an effect of suppressing anodic dissolution.

(B) Like Sn, Sb is also effective in suppressing the anodic dissolution reaction of steel.
(C) Cu is effective in improving weather resistance even in an environment where the amount of incoming salt is large, and the effect is also exhibited in the presence of Sn or Sb.

  (D) On the other hand, when Ni is added in combination with Sn or Sb, there is no effect of improving the corrosion resistance in an environment with a large amount of incoming salt, and if added in a large amount, Ni deteriorates the weather resistance. This behavior of Ni is contrary to the conventional knowledge that weather resistance improves as the amount of Ni added increases. However, in order to prevent deterioration of hot workability due to Cu, that is, so-called Cu embrittlement, it is effective to add a small amount of Ni while being limited to ½ or less of the Cu addition amount.

  (E) When Cr is added alone, it degrades the weather resistance in an environment with a large amount of incoming salt, but when combined with Sn or Sb, it improves the weather resistance in an environment with a large amount of incoming salt. Demonstrate the effect.

(F) When Al is contained, the beach weather resistance is improved.
(G) N dissolves as ammonia and has the effect of raising the pH of the corrosion interface. In an environment with a large amount of incoming salt, the pH decreases due to the hydrolysis of the Fe ³⁺ , but the inclusion of N suppresses the pH decrease at the corrosion interface and improves beach weather resistance.

  (H) Even if one or more selected from Ti, Nb, Mo, W, V, Ca and Mg are contained in the material containing the above components (a) to (g), Effective in improving weather resistance.

(I) Furthermore, when REM is contained, the weldability of the steel material is improved.
The present invention has been completed based on the above findings.
Here, the present invention is, by mass%, C: 0.001 to 0.15%, Si: 2.5% or less, Mn: more than 0.5 to 2.5%, P: less than 0.03%, S: 0.005% or less, Cu: 0.05-1.0%, Ni: 0.01-0.5%, Cr: 0.01-3.0%, Al: 0.003-2.5 % And N: 0.001 to 0.1%, Sn and / or Sb: 0.03 to 0.50%, the balance is Fe and impurities, and Ni / Cu is 0.5 or less A steel material excellent in beach weather resistance, characterized by having a composition.

  The steel composition is, in mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.1%, Mo: 0.01 to 1.0%, W: 0.01 to 1. One or more selected from the group consisting of 0%, V: 0.01-1.0%, Ca: 0.0001-0.1% and Mg: 0.0001-0.1%, and And / or REM: 0.0001% to 0.02% may be further contained.

The steel material excellent in beach weather resistance according to the present invention may be coated with an anticorrosive film on the surface.
The present invention further relates to a structure made from the steel material.

  The steel material of the present invention has sufficient weather resistance in an environment with a large amount of incoming salt, and is optimal as a material with excellent beach weather resistance. As a minimum maintenance material to be used for structures such as bridges in the area to be used, it can be widely applied in the civil engineering and construction fields.

  Below, the effect of the alloy element contained in the steel material of this invention is demonstrated with the reason which limited the content as mentioned above. In the following description, the alloy element content “%” means “mass%”.

C: 0.001 to 0.15%
C is an alloying element necessary for ensuring the strength of steel, but if contained in a large amount, the weldability of the steel material deteriorates. Therefore, the upper limit of the C content is 0.15%. Further, if the content is less than 0.001%, a predetermined strength cannot be secured, so the lower limit is made 0.001%. A desirable range is 0.005% to 0.15%.

Si: 2.5% or less Si is an element that improves the weather resistance as well as an alloy element necessary for deoxidation at the time of steelmaking. If the content exceeds 2.5%, the toughness of the steel is impaired. Therefore, the content is not more than 2.5%. The lower limit is not particularly defined, but if the content is too small, deoxidation is not sufficiently performed. Therefore, when Al is not contained, it is desirable to contain 0.1% or more.

Mn: More than 0.5% to 2.5% or less Mn is an element having an effect of increasing the strength of steel at a low cost, but combines with S to form MnS, and this MnS becomes a starting point of corrosion. , Deteriorate the corrosion resistance and thus the weather resistance. When the amount of S in steel is low, it generally has an effect of improving the weather resistance in a high flying salinity environment. However, although the mechanism is unknown, when it coexists with Ni, if it exceeds 2.5%, the weather resistance deteriorates. Therefore, the content is not more than 2.5%. Desirably, it is 1.5% or less. In order to maintain the strength as structural steel, it is desirable to contain 0.5% or more.

P: Less than 0.03% P is an element that significantly improves the weather resistance. However, if it is excessively contained, the weldability deteriorates. Therefore, the content is made less than 0.03%. The lower limit is not particularly defined, but is preferably 0.005% or more in order to exhibit the effect of improving weather resistance.

S: 0.005% or less S is bonded to Mn to form MnS of non-metallic inclusions, which tends to be a starting point of corrosion and deteriorates weather resistance. Therefore, S needs to be reduced as much as possible. Therefore, the upper limit is made 0.005%.

Cu: 0.05-1.0%
Cu is a basic element for improving the weather resistance, and when 0.05% or more is contained, the weather resistance is improved. However, even if the content exceeds 1.0%, not only the effect is saturated but also Cu embrittlement occurs. Therefore, the content is set to 0.05 to 1.0%.

Ni: 0.01-0.5%
Ni has been attracting attention as an element that remarkably improves the corrosion resistance (beach weather resistance) in an environment with a large amount of incoming salt, and has been developed and put into practical use as a Ni-based weathering steel. However, although the reason is not clear, when Sn and Sb are added together, there is no effect of improving the corrosion resistance, but rather the adverse effect of reducing the effect of improving the weather resistance by Sn and Sb appears. This adverse effect of Ni becomes significant when the Ni content exceeds 0.5% or exceeds 1/2 of the Cu content. However, in order to prevent hot workability deterioration due to Cu addition, so-called Cu embrittlement, addition of 0.01% or more of Ni is necessary. Therefore, in the present invention, the Ni content is limited to a very small amount of 0.01 to 0.5%, and Ni is added so that the Ni / Cu mass ratio is 0.5 or less. It is economically advantageous to reduce the expensive Ni content. Preferably, Ni: 0.01% or more and less than 0.4%.

Cr: 0.01 to 3.0%
Cr can be expected to improve the corrosion resistance due to the formation of protective rust in an environment where the amount of flying salt is not so large, but it promotes the anodic dissolution reaction of steel and degrades the weather resistance in an environment where the amount of flying salt is large.

  However, as will be described later, when Sn or Sb is contained, the effect of improving the weather resistance due to the Cr content is exhibited even in an environment with a large amount of incoming salt. This effect is exhibited when the content is 0.01% or more. However, if the content exceeds 3.0%, the local corrosion susceptibility increases and weldability deteriorates. Therefore, the Cr content is set to 0.01 to 3.0%. A desirable range of the content is 0.5 to 3.0%.

Al: 0.003 to 2.5%
When Al is contained in an amount of 0.003% or more, the weather resistance is improved. However, when the content exceeds 2.5%, the effect is saturated. Therefore, the Al content is 0.003 to 2.5%. In addition, since steel will be easily embrittled if added in a large amount, the upper limit of the content is desirably 2.0%.

N: 0.001 to 0.1%
N dissolves as ammonia and has an effect of improving the weather resistance in a salt environment by suppressing the pH drop due to the hydrolysis of Fe ^{3+ in} an environment with a large amount of incoming salt. This effect is obtained by containing 0.001% or more, and when it exceeds 0.1%, it is saturated. Therefore, the N content is set to 0.001 to 0.1%. A desirable range of the content is 0.002 to 0.08%.

Sn and / or Sb: 0.03 to 0.50%
Sn dissolves as Sn ²⁺ and has an action of inhibiting corrosion by an inhibitor action in an acidic chloride solution. Further, by reducing Fe ³⁺ quickly and reducing the concentration of Fe ³⁺ as an oxidizing agent, the corrosion promoting action of Fe ³⁺ is suppressed, so that the weather resistance in a high flying salinity environment is improved.

  Sn also has the effect of suppressing the anodic dissolution reaction of steel and improving the corrosion resistance. Furthermore, by containing Sn, the effect of improving the weather resistance of Cr is exhibited even in an environment with a large amount of incoming salt.

  When Sn is added alone, these effects become remarkable when the content is 0.03% or more. However, if it exceeds 0.5%, it causes embrittlement. Therefore, the content is made 0.03% to 0.5%. The desirable range of the content is 0.03 to 0.2%.

On the other hand, Sb suppresses the anodic dissolution reaction of steel and suppresses the hydrogen gas generation reaction and the reduction reaction of Fe ³⁺ , thereby improving the weather resistance in a high flying salinity environment. Furthermore, by containing Sb, the effect of improving the weather resistance of Cr is exhibited even in an environment with a large amount of incoming salt.

  When Sb is added alone, these effects become remarkable when the content is 0.03% or more, and when it exceeds 0.5%, the toughness is remarkably deteriorated. Therefore, the content is set to 0.03 to 0.5%. A desirable content is 0.03 to 0.3%.

  When Sn and Sn are added in combination, if the total value is less than 0.03%, the effect of improving the weather resistance in a high flying salinity environment does not appear remarkably, and 0.50% is added. If exceeded, the toughness of the steel deteriorates. Therefore, the total content of Sn and Sn is set to 0.03 to 0.5%. A desirable total content is 0.03 to 0.3%.

  The steel material of the present invention further contains one or more selected from the group consisting of Ti, Nb, Mo, W, V, Ca and Mg, and / or REM in addition to the above alloy elements. Also good. The reason why the contents of these elements are limited as described above is as follows.

Ti: 0.01 to 0.3%
Ti forms TiC to fix C, suppresses the formation of chromium carbide and improves the weather resistance, and suppresses the formation of MnS as a starting point of corrosion due to the formation of TiS. This effect appears when the content is 0.01% or more. When the content exceeds 0.3%, the effect is not only saturated, but the cost of the steel material is increased. Therefore, when Ti is contained, the content is set to 0.01 to 0.3%.

Nb: 0.01-0.1%
Nb, like Ti, has the effect of improving weatherability by forming NbC and suppressing the formation of chromium carbides. This effect appears when the content is 0.01% or more, and is saturated when the content exceeds 0.1%. For this reason, when Nb is contained, the content is set to 0.01 to 0.1%.

Mo: 0.01-1.0%
Mo is an element that dissolves and adsorbs to rust in the form of oxygenate ions MoO ₄ ²⁻ , suppresses permeation of chloride ions in the rust layer, and improves corrosion resistance. This effect is obtained when the content in the steel is 0.01% or more. However, when the content exceeds 1.0%, the effect is not only saturated, but the cost of the steel material is increased. Therefore, when Mo is contained, the content is set to 0.01 to 1.0%.

W: 0.01-1.0%
W, like Mo, dissolves and exists in the form of oxygenate ions, suppresses permeation of chloride ions in the rust layer, and improves corrosion resistance. This effect appears when the content is 0.01% or more, and when it exceeds 1.0%, not only is the content saturated, but the cost of the steel material increases. Therefore, when W is contained, the content is set to 0.01 to 1.0%.

V: 0.01-1.0%
V, like Mo and W, dissolves and exists in the form of oxyacid ions, suppresses permeation of chloride ions in the rust layer, and improves corrosion resistance. This effect appears when the content is 0.01% or more, and is saturated when the content exceeds 1.0%. Therefore, when V is contained, the content is set to 0.01 to 1.0%.

Ca: 0.0001-0.1%
Ca exists in the form of an oxide in steel, and has an effect of suppressing the promotion of corrosion by suppressing the decrease in pH at the interface in the corrosion reaction part. This effect can be obtained by adding 0.0001% or more, but when it exceeds 0.1%, it is saturated. Therefore, when Ca is contained, the content is 0.0001 to 0.1%.

Mg: 0.0001-0.1%
Mg, like Ca, suppresses the decrease in pH at the interface in the corrosion reaction part and improves the corrosion resistance. This effect can be obtained by adding 0.0001% or more, but when it exceeds 0.1%, it is saturated. Therefore, when Mg is contained, the content is set to 0.0001 to 0.1%.

REM: 0.0001-0.02%
REM is contained for the purpose of improving the weldability of steel. The effect is exhibited when the content is 0.0001% or more, and when the content exceeds 0.02%, the effect is saturated. For this reason, when it contains REM, the content shall be 0.0001 to 0.02%.

  The steel material of the present invention is a steel material containing the above essential elements and optional elements, with the balance being Fe and impurities. Note that steel in which inclusions such as oxide are finely dispersed in the steel is also included in the steel material of the present invention.

  The steel material of the present invention can have various shapes including deformed materials such as plate materials, pipe materials, bar materials, and H-shaped steel. In general, the thickness is preferably 3 mm or more. The weathering steel is generally a hot rolled material, but the hot rolling conditions for producing the steel of the present invention are not particularly limited and may be the same as usual.

  When further improving the weather resistance, it is desirable to cover the surface of the steel material of the present invention with an anticorrosion film. The anticorrosion film used in the present invention means a film applied for the purpose of anticorrosion of steel materials. Specifically, various types of rust stabilization coatings (including a chemical conversion treatment system and a coating system) well-known in weathering steel materials; anticorrosion plating films such as Zn plating, Al plating, Zn-Al plating; Zn spraying, Al Includes metal spray coatings such as spraying; general anti-corrosion coatings such as vinyl butyral, epoxy, urethane, and phthalic acid. Even when any anticorrosion film is applied, excellent weather resistance and high anticorrosion performance can be exhibited. The film thickness or adhesion amount of these anticorrosion films is not particularly limited, and may be within a normal range.

  As described above, since the steel material of the present invention exhibits excellent beach weather resistance in an environment with a large amount of incoming salt, it is suitable for structures such as bridges in beach areas and areas where snow melting salt / freezing agents are sprayed. It can be used as a minimum maintenance material that does not require painting. This type of structure is generally produced by forming, such as cutting and bending, and welding, but the steel material of the present invention is also excellent in workability and weldability.

  No. 1 to No. 20 steels having the chemical compositions shown in Table 1 were melted in a 150 kg vacuum melting furnace, forged ingots, then heated and rolled, and were 4 mm thick x 150 mm wide x long. A steel material having a thickness of 1000 mm was produced. Next, the front and back surfaces of the steel material were mechanically ground, and a test piece having a thickness of 3 mm × width of 60 mm × length of 100 mm was cut out. The oxygen content of the steel material produced in this example was in the range of 0.0001 to 0.005%.

The obtained test piece was evaluated by SAE (Society of Automotive Engineers) J2334 test. SAE J2334 test is wet: 50 ° C., 100% RH, 6 hours, salt adhesion: 0.5% NaCl, 0.1% CaCl ₂ , 0.075% NaHCO ₃ aqueous solution, 0.25 hour, dry: 60 It is an accelerated test with 1 cycle (total 24 hours) at ℃, 50% RH, 17.75 hours, and the corrosion form is said to be similar to the atmospheric exposure test (Hiroo Nagano, Masato Yamashita, Hitoshi Uchida) : Environmental Materials Science, Kyoritsu Shuppan (2004), p.74). This test simulates a severe corrosive environment in which the amount of incoming salt exceeds 1 mdd.

  After 120 cycles of the SAE J2334 test, the rust layer on the surface of each test piece was removed, and the thickness reduction was measured. The test results are shown in Table 1. “Corrosion weight loss” in the table is an average reduction in the thickness of the test piece, and is calculated using the weight reduction before and after the test and the surface area of the test piece.

  As is clear from the results in Table 1, since Comparative Example (No. 24) has a high Mn content, Ni, Sn, and Sb coexist in Comparative Example (No. 26), and Ni / Cu is 0.5. Therefore, in Comparative Examples (No. 27, No. 28), the amount of Cr, Cu, Ni, Sn, and Sb was small, so the amount of corrosion increased. Moreover, since comparative example (No. 29) has little content of Cr, Cu, and Ni, and comparative example (No. 30) has little content of Cr and Cu, the corrosion amount became large. Comparative Example No. For 25, the test was stopped because many cracks occurred during rolling.

  In all the examples of the present invention, the content of components specified in the present invention is satisfied, so the corrosion weight loss is as small as 0.20 mm or less.

Claims (5)

  By mass%, C: 0.001 to 0.15%, Si: 2.5% or less, Mn: more than 0.5%, 2.5% or less, P: less than 0.03%, S: 0.005 %: Cu: 0.05-1.0%, Ni: 0.01-0.5%, Cr: 0.01-3.0%, Al: 0.003-2.5%, and N: A composition containing 0.001 to 0.1%, Sn and / or Sb: 0.03 to 0.50%, the balance being Fe and impurities, and a Ni / Cu mass ratio of 0.5 or less. A steel material excellent in beach weather resistance, characterized by having.   Furthermore, by mass%, Ti: 0.01-0.3%, Nb: 0.01-0.1%, Mo: 0.01-1.0%, W: 0.01-1.0%, The composition contains one or more selected from the group consisting of V: 0.01-1.0%, Ca: 0.0001-0.1% and Mg: 0.0001-0.1%. 1. A steel material having excellent beach weather resistance according to 1.   Furthermore, the steel material excellent in the beach weather resistance of Claim 1 or 2 which contains 0.0001%-0.02% of REM by the mass%.   The steel material according to any one of claims 1 to 3, wherein the surface is coated with an anticorrosive film.   The structure produced from the steel materials in any one of Claims 1-4.